Control method of a flotation machine that is used in metallurgical processes

ABSTRACT

The invention relates to a method of using a flotation machine that is used in metallurgical processes and to a flotation machine. The flotation machine foams hydrophobic particles from an aqueous slurry that contains these particles. The flotation machine includes a flotation cell ( 1 ), and a rotor ( 2 ) that is inside the flotation cell. The rotor ( 2 ) is rotated at a mixing power, which maintains the suspension in the slurry and mixing of air with the slurry to form the foam, and the mixing power is controlled by adjusting the rotation speed of the rotor. The amount of solid matter S accumulated on the bottom of the cell ( 1 ) is determined, and the rotation speed of the rotor ( 2 ) is adjusted on the basis of the determined amount of solid matter. The flotation machine includes a measuring device ( 5 ) for determining the amount of solid matter accumulated on the bottom of the cell. The adjusting device ( 4 ) is arranged to adjust the rotation speed of the motor ( 3 ), which rotates the rotor ( 2 ), on the basis of the measuring result of the measuring device ( 5 ) to remove the solid matter from the bottom of the cell.

FIELD OF THE INVENTION

The invention relates to a method defined in the preamble of claim 1.The invention further relates to a flotation machine defined in thepreamble of claim 5.

BACKGROUND OF THE INVENTION

In well-known metallurgical flotation methods and flotation machines,particles that are rendered hydrophobic are foamed from an aqueousslurry that contains these particles. The flotation machine includes aflotation cell and a rotor that is inside the flotation cell. The rotoris rotated at a mixing power, which maintains a suspension in the slurryand the mixing of air with the slurry, to form the foam. It is furtherknown that the mixing power can be adjusted by adjusting the rotationspeed of the rotor. An electric motor is normally arranged to rotate therotor, and the rotation speed of the motor can be changed by means of afrequency converter that serves as an adjusting device.

When using the flotation machine, so-called sanding occurs; that is,solid matter accumulates on the bottom of the flotation cell, in thecorner region between the bottom and the wall. Excessive accumulation ofsolid matter is not allowed, because the solid matter thus accumulatedtends to block the inlet and outlet openings of slurry that are usuallylocated in the area of accumulation.

In prior art, the matter has been solved in a simple way by selecting“an adequate amount” of mixing power; in other words, the rotor isrotated continuously at a high enough rotation speed, at which the solidmatter does not accumulate excessively. This has often resulted inconsiderable excess power with respect to what is needed and, at thesame time, in poor energy efficiency.

It has been observed that, in many cases, the metallurgical results donot deteriorate, even if the mixing power is reduced, but at some stage,a limiting factor of reducing the mixing power will consist of theexcessive accumulation of solid matter, or sanding, on the bottom of thecell.

The energy efficiency is a very significant matter in flotation plants.For example, in a flotation plant, there can be 50 flotation machines ina series, each having a 300 kW electric motor. When each of them iscontinuously operated with excess power to prevent sanding, we aretalking about a considerable item of expenditure.

OBJECT OF THE INVENTION

The object of the invention is to eliminate the disadvantages mentionedabove.

In particular, the object of the invention is to disclose a method ofoperating a flotation machine and a flotation machine, by means of whichthe problems caused by the accumulation of solid matter are avoided and,at the same time, the operation of the flotation machine becomes asenergy-effective as possible.

SUMMARY OF THE INVENTION

The method according to the invention is characterized in what isdisclosed in claim 1. The flotation machine according to the inventionis characterized in what is disclosed in claim 5.

According to the invention, in the method, the amount of solid matteraccumulated on the bottom of the cell is determined, and the rotationspeed of the rotor is adjusted on the basis of the measured amount ofsolid matter.

Correspondingly, according to the invention, the flotation machineincludes a measuring device for determining the amount of solid matteraccumulated on the bottom of the cell. The adjusting device is arrangedto adjust the rotation speed of the motor on the basis of the measuringresults of the measuring device to remove the solid matter from thebottom of the cell.

The invention is based on the remarkable observation that when theamount of accumulated solids is observed and the mixing power isadjusted accordingly in a controlled manner, the mixing power can evenbe halved, without the metallurgical result weakening, from thecontinuous mixing power, which at present is required to keep theaccumulation of solid matter on the bottom of the cell at the minimum.By means of the invention, the energy efficiency of the flotation can beconsiderably improved and significant cost savings can be achieved. Themixing power can also be optimized in real time regarding the sanding,whereby the energy efficiency of the flotation machine can be optimizedin its entirety.

In an embodiment of the method, the rotation speed of the rotor iscontinuously kept at the lowest possible standard value, at which thedetermined amount of solid matter accumulated on the bottom of the cellwill not exceed a predetermined limit value.

In an embodiment of the method, the rotor is rotated at the lowestpossible first rotation speed which, in terms of metallurgy, is selectedso as to have an adequate mixing power to maintain the suspension andform the foam and, at the same time, to be small enough to allow theaccumulation of solid matter on the bottom of the cell. The amount ofsolid matter accumulated on the bottom of the cell is furtherdetermined. The determined amount of solid matter is compared with apredetermined limit value. If the determined amount of solid matterexceeds the predetermined limit value, the rotation speed of the rotoris increased to a second rotation speed, which is higher than the firstrotation speed and which is adequate to remove the solid matter that isaccumulated on the bottom of the cell. The second rotation speed ismaintained so long that the amount of solid matter is below thepredetermined limit value, and the rotation speed can again be reducedto the lower first rotation speed.

It is, indeed, preferable to allow a minor accumulation of solid matter,because the layer of solid matter functions as an autogenous protectivelayer that protects the bottom against wearing. Thus, it is notnecessary to protect the bottom, for example, with paint or the like.

In an embodiment of the method, the rotor is rotated at the lowestpossible first rotation speed which, in terms of metallurgy, is selectedso as to have an adequate mixing power to maintain the suspension andform the foam and, at the same time, to be small enough to allow theaccumulation of solid matter on the bottom of the cell. The rotationspeed of the rotor is periodically or randomly increased from the firstrotation speed to the higher second rotation speed to remove the solidmatter accumulated on the bottom of the cell. The second rotation speedis maintained for a predetermined period of time, after which therotation speed of the rotor is reduced to the said first rotation speed.

In an embodiment of the flotation machine, the measuring device is onethat is based on the echo sounding of the surface of the solid matter.The measuring device that is based on echo sounding can be, for example,an ultrasonic radar. The ultrasonic radar is preferably placed on thebottom of the cell.

In an embodiment of the flotation machine, the measuring device includesa sonic detector, which is adapted so as to recognize the sound made bythe solid matter that is accumulated on the bottom of a container. Thesonic detector can comprise, for example, microphones which are placedon the wall of the cell at different heights with respect to the bottom,corresponding to the predetermined limit values of the level of thesolid matter layer.

LIST OF FIGURES

In the following, the invention is described in detail by means ofapplication examples and with reference to the appended drawing, whichshows a schematic cross section of an embodiment of the flotationmachine, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment of the flotation machine. The invention is,however, not limited to the flotation machine according to the figure.The flotation machine includes a flotation cell 1. The flotation cell 1has a mainly cylindrical shape and its interior is limited below by abottom 7 and on the side by a side wall 10. A rotor 2 is centrallyarranged inside the flotation cell in the vicinity of bottom 7. Therotor 2 comprises air distribution holes, through which air isdistributed into the slurry during mixing to form foam in the slurry,when the rotor rotates around its vertical axis. The rotor 2 is rotatedby an electric motor 3. The rotation speed of the motor 3 can be changedby means of an adjusting device 4. Slurry is fed into the cell 1 throughan inlet I that can be opened and closed (shown by a dotted line in thefigure) and removed through an outlet 0 that can be opened and closed(shown by a dotted line in the figure). Foam and the substances to berecovered that are stuck thereto exit through an overflow OF.

Furthermore, the flotation machine includes a measuring device 5 fordetermining the amount of solid matter accumulated on the bottom of thecell. The adjusting device 4 is arranged to adjust the rotation speed ofthe motor 3 on the basis of the measuring result of the measuring device5 to remove the solid matter S from the bottom of the cell.

In the figure, an embodiment of the measuring device 5 is outlined by adashed line, being herein a measuring device 6 that is based on the echosounding of the surface of the solid matter. It can be, for example, anultrasonic radar 6. The ultrasonic radar 6 is placed on the bottom 7 ofthe cell 1 on the outside, or it can penetrate the bottom. Theultrasonic radar 6 can measure the level, on which the solid mattersurface is situated.

Another example of the measuring device 5 in the figure is the sonicdetector 8 that is drawn by a dot-and-dash line and adapted so as torecognize the sound caused by the solid matter that is accumulated onthe bottom of the container, the sound being created by the solid matterflow rubbing against the side wall 10 of the cell. The sonic detector 8can include several microphones 9, which are placed on the wall 10 ofthe cell at different heights with respect to the bottom 7,corresponding to the predetermined limit values of the level of thesolid matter layer. The velocity profile of the flow inside the cell 1can also be calculated from an acoustic correlation, when so desired.

The equipment mentioned above is used so that the amount of solid matteraccumulated on the bottom of the cell is determined by the measuringdevice 5. The measuring device 5 delivers a signal related to the amountof solid matter to the adjusting device 4, which adjusts the rotationspeed of the motor 3 that drives the rotor 2, on the basis of thedetermined amount of solid matter accumulated on the bottom.

The mixing power can be controlled, for example, so that the rotationspeed of the rotor 2 is continuously kept at the lowest possiblestandard value, at which the determined amount of solid matter Saccumulated on the bottom 7 of the cell will not exceed thepredetermined limit value.

The mixing power can also be controlled, for example, so that the rotor2 is rotated at the lowest possible first rotation speed which, in termsof metallurgy, is selected so as to have an adequate mixing power tomaintain the suspension and form the foam and, at the same time, to besmall enough to allow the accumulation of solid matter S on the bottomof the cell 1. The amount of solid matter accumulated on the bottom 7 ofthe cell 1 is determined and the determined amount of solid matter S iscompared with a predetermined limit value. If the determined amount ofsolid matter S exceeds the predetermined limit value, the rotation speedof the rotor 2 is increased to the second rotation speed, which ishigher than the first rotation speed and which is adequate to remove thesolid matter that is accumulated on the bottom of the cell. The secondrotation speed is maintained until the amount of solid matter is belowthe predetermined limit value and, finally, the rotation speed isreduced to the first rotation speed and kept at that, until thedetermined amount of solid matter S again exceeds the predeterminedlimit value.

The equipment can also be used so that the rotor 2 is rotated at thelowest possible first rotation speed which, in terms of metallurgy, isselected so as to have an adequate mixing power to maintain thesuspension and form the foam and, at the same time, to be small enoughto allow the accumulation of solid matter on the bottom of the cell. Therotation speed of the rotor 2 is increased randomly or periodically (forexample, once in an hour, once in 24 hours) from the first rotationspeed to the higher second rotation speed to remove the solid matter Saccumulated on the bottom of the cell, and the second rotation speed ismaintained for a predetermined period of time, after which the rotationspeed of the rotor is reduced to the said first rotation speed.

The invention is not limited to the application examples described aboveonly, but many modifications are possible within the inventive ideadefined by the claims.

1. A method of using a flotation machine that is used in metallurgical processes, the flotation machine foaming hydrophobic particles from an aqueous slurry that contains these particles, and the flotation machine including a flotation cell (1) and a rotor (2), which is inside the flotation cell and in which the rotor is rotated at a mixing power that maintains a suspension in the slurry and mixing of air with the slurry to form foam, and the mixing power is controlled by adjusting the rotation speed of the rotor, characterized in that the rotor is rotated at the lowest possible first rotation speed which, in terms of metallurgy, is selected so as to have an adequate mixing power to maintain a suspension and form foam and, at the same time, to be small enough to allow the accumulation of solid matter on the bottom of the cell; the amount of solid matter accumulated on the bottom of the cell is determined; the determined amount of solid matter is compared with the predetermined limit value; if the determined amount of solid matter exceeds the predetermined limit value, the rotation speed of the rotor is increased to a second rotation speed, which is higher than the first rotation speed and which is adequate to remove the solid matter accumulated on the bottom of the cell; and the second rotation speed is maintained, until the amount of solid matter is below the predetermined limit value, and the rotation speed is reduced to the first rotation speed.
 2. A method according to claim 1, characterized in that the rotation speed of the rotor is continuously kept at the lowest possible standard value, at which the determined amount of solid matter accumulated on the bottom of the cell will not exceed a predetermined limit value.
 3. A method according to claim 1, characterised in that the rotor is rotated at the lowest possible first rotation speed which, in terms of metallurgy, is selected so as to have an adequate mixing power to maintain a suspension and form foam and, at the same time, to be small enough to allow the accumulation of solid matter on the bottom of the cell; the rotation speed of the rotor is periodically increased from the first rotation speed to the higher second rotation speed to remove the solid matter accumulated on the bottom of the cell; and the second rotation speed is maintained for a predetermined period of time, after which the rotation speed of the rotor is reduced to the said first rotation speed.
 4. A flotation machine for floating hydrophobic particles from an aqueous slurry that contains these particles, comprising a flotation cell (1); a rotor (2), which is arranged to rotate inside the flotation cell for distributing air into the slurry to form foam and to mix the slurry; a motor (3) for rotating the rotor; and an adjusting device (4) for changing the rotation speed of the rotor, characterized in that the flotation machine includes a measuring device (5) for determining the amount of solid matter accumulated on the bottom of the cell; that the adjusting device (4) is arranged to adjust the rotation speed of the motor (3) on the basis of the measuring result of the measuring device (5) to remove the solid matter from the bottom of the cell; and that the adjusting device (4) is arranged to adjust the rotor to rotate at the lowest possible first rotation speed which, in terms of metallurgy, is selected so as to have an adequate mixing power to maintain a suspension and form foam and, at the same time, to be small enough to allow the accumulation of solid matter on the bottom of the cell, the measuring device (5) is arranged to determine the amount of solid matter accumulated on the bottom of the cell, and, if the determined amount of solid matter exceeds the predetermined limit value, the adjusting device (4) is arranged to increase the rotation speed of the rotor to a second rotation speed, which is higher than the first rotation speed and which is adequate to remove the solid matter accumulated on the bottom of the cell, and the second rotation speed is arranged to be maintained until the amount of solid matter is below the predetermined limit value, and the adjusting device (4) is arranged to reduce the rotation speed to the first rotation speed.
 5. A flotation machine according to claim 4, characterized in that the measuring device (5) is a measuring device (6) that is based on the echo sounding of the surface of the solid matter.
 6. A flotation machine according to claim 5, characterized in that the measuring device that is based on echo sounding is an ultrasonic radar (6).
 7. A flotation machine according to claim 6, characterized in that the ultrasonic radar (6) is placed on the bottom (7) of the cell (1).
 8. A flotation machine according to claim 4, characterized in that the measuring device (5) includes a sonic detector (8), which is adapted to recognize the sound caused by the solid matter that is accumulated on the bottom of the container.
 9. A flotation machine according to claim 8, characterized in that the sonic detector (8) includes micro-phones (9), which are placed on the wall (10) of the cell at different heights with respect to the bottom (7), corresponding to the predetermined limit values of the level of the solid matter layer. 